87,787 research outputs found
Preface of the book: Fraternali, F., Rimoli, J.J. (eds) Tensegrity Systems. CISM International Centre for Mechanical Sciences, vol 2. Springer, Cham. https://doi.org/10.1007/978-3-031-82283-4_9
No full textThis book presents topics from an advanced course held at the International Center for Mechanical Sciences in Udine, Italy, in September 2024. It aims to illustrate the unique mechanical behaviors of tensegrity systems and their applications in mechanical metamaterials, space structures, and biomechanical models. Several studies have shown that by controlling the mechanical response of tensegrity structures through internal and external prestress, it is possible to adjust the speed of mechanical waves within these systems, creating tunable bandgap structures. Furthermore, the geometrically nonlinear response exhibited by several tensegrity systems allows for the support of either compression or rarefaction solitary wave dynamics. These behaviors can be effectively utilized to design novel devices capable of focusing mechanical waves in narrow regions of space, as well as i9nnovative impact protection systems
A Multiscale Approach to the Elastic Moduli of Biomembrane
Full text linkWe develop equilibrium fluctuation formulae for the isothermal elastic moduli of discrete biomembrane models at different scales. We account for the coupling of large stretching and bending strains of triangulated network models endowed with harmonic and dihedral angle potentials, on the basis of the discrete-continuum approach presented in Schmidt and Fraternali (J Mech Phys Solids 60:172–180, 2012). We test the proposed equilibrium fluctuation formulae with reference to a coarse-grained molecular dynamics model of the red blood cell (RBC) membrane (Marcelli et al. in Biophys J 89:2473–2480, 2005; Hale et al. in Soft Matter 5:3603–3606, 2009), employing a local maximum-entropy regularization of the fluctuating configurations (Fraternali et al. in J Comput Phys 231:528–540, 2012). We obtain information about membrane stiffening/softening due to stretching, curvature, and microscopic undulations of the RBC model. We detect local dependence of the elastic moduli over the RBC membrane, establishing comparisons between the present theory and different approaches available in the literature
F. Fraternali, Dispositivo di isolamento sismico (“Seismic isolator device“), Brevetto Italiano No. 102015000015521, Concesso in data 25 Ottobre, 2017, Depositato in data 18 Maggio, 2015. European Patent No. EP3298217, Granted May 1, 2019 (PCT publication number WO2016185376).
No full textSeismic isolator device shaped to be positioned at the base of a building to absorb a
vibration resulting from a seismic movement, comprising a layered structure (100) wherein an
intermediate layer (12) made of a pentamode material is comprised between an upper laminar
element and a lower laminar element made of a rigid material
The Galactic fountain as an origin for the Smith Cloud
Full text linkThe recent discovery of an enriched metallicity for the Smith high-velocity H I Cloud (SC) lends support to a Galactic origin for this system. We use a dynamical model of the galactic fountain to reproduce the observed properties of the SC. In our model, fountain clouds are ejected from the region of the disc spiral arms and move through the halo interacting with a pre-existing hot corona. We find that a simple model where cold gas outflows vertically from the Perseus spiral arm reproduces the kinematics and the distance of the SC, but is in disagreement with the cloud's cometary morphology, if this is produced by ram-pressure stripping by the ambient gas. To explain the cloud morphology, we explore two scenarios: (I) the outflow is inclined with respect to the vertical direction and (II) the cloud is entrained by a fast wind that escapes an underlying superbubble. Solutions in agreement with all observational constraints can be found for both cases, the former requires outflow angles >40° while the latter requires ≳1000 km s-1 winds. All scenarios predict that the SC is in the ascending phase of its trajectory and has large - but not implausible - energy requirements
Angular momentum, accretion, and radial flows in chemodynamical models of spiral galaxies
Full text linkGas accretion and radial flows are key ingredients of the chemical evolution of spiral galaxies. They are also tightly linked to each other (accretion drives radial flows due to angular momentum conservation) and should therefore be modeled simultaneously. We summarize an algorithm that can be used to consistently compute accretion profiles, radial flows, and abundance gradients under quite general conditions, and we describe illustrative applications to the Milky Way. We find that gas-phase abundance gradients strongly depend on the angular momentum of the accreting material and, in the outer regions, they are significantly affected by the choice of boundary conditions
On the origin of the warm-hot absorbers in the Milky Way's halo
Full text link<p>Disc galaxies like the Milky Way are expected to be surrounded by massive coronae of hot plasma that may contain a significant fraction of the so-called missing baryons. We investigate whether the local (vertical bar v(LSR)vertical bar <400 km s(-1)) warm-hot absorption features observed towards extra-Galactic sources or halo stars are consistent with being produced by the cooling of the Milky Way's corona. In our scheme, cooling occurs at the interface between the disc and the corona and it is triggered by positive supernova feedback. We combine hydrodynamical simulations with a dynamical 3D model of the galactic fountain to predict the all-sky distribution of this cooling material, and we compare it with the observed distribution of detections for different 'warm' (Si iii, Si iv, C ii, C iv) and 'hot' (O vi) ionized species. The model reproduces the position-velocity distribution and the column densities of the vast majority of warm absorbers and about half of O vi absorbers. We conclude that the warm-hot gas responsible for most of the detections lies within a few kiloparsec from the Galactic plane, where high-metallicity material from the disc mixes efficiently with the hot corona. This process provides an accretion of a few M-circle dot yr(- 1) of fresh gas that can easily feed the star formation in the disc of the Galaxy. The remaining O vi detections are likely to be a different population of absorbers, located in the outskirts of the Galactic corona and/or in the circumgalactic medium of nearby galaxies.</p>
Parameter optimized surfaces (POPS): analysis of key interactions and conformational changes in the ribosome
No full textWe present a new method for the calculation of solvent accessible surface areas at the atomic and residue levels, which we call parameter optimized surfaces (POPS-A and POPS-R ). Atomic and residue areas (the latter simulated with a single sphere centered at the C(alpha)s atom for amino acids and at the P atom for nucleotides) have been optimized versus accurate all-atoms methods. We concentrated on an analytical formula for the approximation of solvent accessibilities. The formula is simple, easily derivable and fast to compute, therefore it is practical for use in molecular dynamics simulations as an approximation to the first solvation shell. The residue based approach POPS-R has been derived as a useful tool for the analysis of large macromolecular assemblies like the ribosome, and is especially suited for use in refinement of low resolution structures. The structures of the 70S, 50S and 30S ribosomes have been analyzed in detail and most of the interactions within the subunits and at their interfaces were clearly identified. Some interesting differences between 30S alone and within the 70S have been highlighted. Owing to the presence of the P-tRNA in the 70S ribosome, localized conformational rearrangements occur within the subunits, exposing Arg and Lys residues to negatively charged binding sites of P-tRNA. POPS-R also allows for estimates of the loss of free energy of solvation upon complex formation, particularly useful in designing new protein-RNA complexes and in suggesting more focused experimental wor
Efficiency of gas cooling and accretion at the disc-corona interface
Full text linkIn star-forming galaxies, stellar feedback can have a dual effect on the circumgalactic medium both suppressing and stimulating gas accretion. The trigger of gas accretion can be caused by disc material ejected into the halo in the form of fountain clouds and by its interaction with the surrounding hot corona. Indeed, at the disc-corona interface, the mixing between the cold/metal-rich disc gas (T ≲ 104 K) and the hot coronal gas (T ≳ 106 K) can dramatically reduce the cooling time of a portion of the corona and produce its condensation and accretion. We studied the interaction between fountain clouds and corona in different galactic environments through parsec-scale hydrodynamical simulations, including the presence of thermal conduction, a key mechanism that influences gas condensation. Our simulations showed that the coronal gas condensation strongly depends on the galactic environment, in particular it is less efficient for increasing virial temperature/mass of the haloes where galaxies reside and it is fully ineffective for objects with virial masses larger than 1013 M⊙. This result implies that the coronal gas cools down quickly in haloes with low-intermediate virial mass (Mvir ≲ 3 × 1012 M⊙) but the ability to cool the corona decreases going from late-type to early-type disc galaxies, potentially leading to the switching off of accretion and the quenching of star formation in massive systems
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